The goal of the investigative team is to examine the effects of sympathetic nervous system activation during exercise. A specific goal of this proposal is to examine the role of the sympathetic nervous system in modulating blood flow to skeletal muscle during exercise. It is our general hypothesis that vascular conductance in exercising skeletal muscle is tightly linked to cardiac output. Previous studies have shown that increased sympathetic nervous tone plays an important role in constricting dialated skeletal muscle muscle blood vessels during exercise preventing a fall in BP. One of the mechanisms to stimulate the sympathetic nervous system is the baroreceptor system. By applying lower body negative pressure, the baroreceptor is unloaded and the sympathetic nervous system is activated. The specific aims and hypothesis of this study are: 1) exercise alone and in combination with lower body negative pressure will serve to systematically activate the sympathetic nervous system. This will lower flow and accentuate anaerobic glycolysis in the muscle. Pharmacological procedures can be used to selectively block sympathetic tone to a particular region, including exercising limbs. Stellate ganglion blockade is an example of such a method that provides a way to block sympathetic nerve activity to the upper extremity. This method combined with lower body negative pressure permits observing the systemic effects of sympathetic nervous system during exercise despite blocking signals from the exercising forearm.